Jon Hamm found it "incredibly hard" watching his mother lose her battle with cancer.
The 'Mad Men' star was just 10 years old when his beloved parent - who divorced his father when he was two - was diagnosed with the disease and he couldn't believe how much it affected her in a short space of time.
Speaking in the new UK issue of GQ magazine, he said: "I remember watching my father and my grandmother and grandfather completely lose their s**t.
"These people who were usually so composed, so put together, so adult. I just remember thinking, 'This can't be good.'
"It was very fast. It was incredibly hard to watch. Life really does a number on you. I watched my mum shrivel up, and at 35. She was this incredibly healthy, beautiful woman and by the time she died she weighed 80lb and looked like she was 70."
Jon then went to live with his father - who died a decade later - and says the toll the tragedy had on him was huge.
The 43-year-old actor explained: "He had been so alive my dad. He had this ability to have a conversation with anyone. He was interested in everyone.
"[Afterwards] he was just so much older, so much sadder. Life was harder."

George Clooney and Amal Alamuddin have obtained their marriage licence.
The couple, who got engaged in April and are tipped to exchange vows at his lavish estate in Lake Como, Italy next month, attained the legal document at Chelsea Town Hall in London, enabling them to make their union official.
The 'Gravity' star's name on the licence, which was reportedly unveiled on a piece of paper behind a glass cover outside the town hall for all to see, reads George Timothy Clooney, while the British lawyer's is listed as Amal Ramazi Alamuddin, according to Dlisted.com.
It was recently claimed that George, 53, wants to hire 'Born to Die' hitmaker Lana Del Rey to perform at his wedding because 36-year-old Amal, who celebrated her bridal shower in New York City last month, is such a big fan.
A source said: "Amal is a massive fan of Lana's, which has made George determined to make this happen.
"He contacted Lana's people to see if she'll perform at their wedding in Italy."
The 'Monuments Men' actor previously insisted he was very lucky to be marrying the human rights lawyer.
He said: "I'm marrying up."

Bruce Willis and Demi Moore's youngest daughter allegedly checked into rehab last month.
Tallulah Willis, who recently admitted she "struggled" with body dysmorphia and an eating disorder when she was younger, reportedly entered The Meadows in Arizona for cocaine and alcohol abuse on July 23.
A source told Star magazine that the 20-year-old blogger, whose mother sought help for "stress and exhaustion" in 2012 after splitting from her third husband, Ashton Kutcher, and for drug and alcohol abuse in the 1980s, secretly began treatment at the famous facility after Demi convinced her to seek help.
According to the magazine, Bruce threatened to cut Tallulah off financially in May after his 23-year-old daughter, Scout, informed him she saw Tallulah using drugs at a party.
But she decided to move to New York City in mid-June instead, where her problems are said to have spiralled out of control until her mother intervened.
The insider added: "Demi had been shocked when Tallulah confessed to her. But she knew enough not to judge. She knew her daughter needed her and she was glad she could be there to help."
A spokesperson for Tallulah, who was arrested when she was 17 for underage drinking, declined to comment to the MailOnline "at this stage."
The blonde beauty recently revealed she always felt "ugly" and was diagnosed with body dysmorphia when she was 13.
She said: "I was trapped in this body. I started starving myself and losing a bunch of weight and I got down to like 95 pounds. When I lost my curves and when my boobs shrivelled up into like nothing and I had no shape. It put me in even more of a cage."
Demi and Bruce, who also have daughter, Rumer, 25, split in 1998 after 11 years of marriage.
The 'Die Hard' actor also has daughters Mabel, two, and Evelyn, three months, with wife Emma Heming.

Diane Kruger wants to grow old in Paris.
The 38-year-old German actress, who has been in a relationship with Joshua Jackson, 36, for eight years, also plans to raise her future children in France, as she finds it more relaxing than Los Angeles.
The 'Bridge' star told InStyle magazine: "I consider myself half French. That's where I think I want to raise my children, where I see myself growing old.
"Maybe because I'm European, their way of life is very close to what I know. I've always loved Paris. When I went there it was my first time ever on a plane. From the moment I arrived, I was like, I'm never leaving."
The blonde beauty can't resist indulging in rich food when she visits friends in the city.
She said: "In L.A., you're the devil if you eat bread. Josh and I went to Paris over Christmas, and he gained, like, 15 pounds. The bread! White chocolate! Risotto! Paté! My friend lives out in Normandy on a farm, and she makes her own foie gras. And then the wine. All we did was eat and drink. It was so fun."
Diane previously insisted she has no plans to marry former 'Dawson's Creek' actor Joshua because of her 2006 divorce from French actor Guillaume Canet.
But the couple are eager to start a family together.
In an interview last year, she said: "I keep dreaming about a baby, but I don't feel any pressure. I never thought about having children in the past, then Josh and I started thinking about a family six months after we became involved."

Blake Lively thinks it would be "a lot of fun" to work with husband Ryan Reynolds again.
The former 'Gossip Girl' star, who married her 'The Green Lantern' co-star in September 2012, wishes she could turn back time and return to the set of the film when they first met in 2010, even though Ryan was still married to his first wife, Scarlett Johansson, at the time.
Asked if she has any plans to make another movie with the heartthrob, the 26-year-old beauty told fans during a Q&A on Vogue.com's Twitter profile: "In the olden days, a couple could be in every movie together, but it's just not like that anymore.
"We both wish we could go back to then, because that would be a lot of fun."
The couple finished shooting the movie in August 2010 and Ryan filed for divorce from Scarlett in December of that year, but he only started dating the 'Savages' beauty in October 2011.
Blake also revealed the most romantic gifts she and Ryan, 37, have ever exchanged during a video for the fashion bible's website.
Discussing the best surprise she's ever planned for someone, she said: "A collection of short stories written by loved ones for my husband."
As for the best present she's ever received, she said: "A video of all the people that had made an impact my life for my birthday from my husband."

50 Cent's bodyguard is being investigated for alleged assault. The 39-year-old rapper was shopping at Burbank Town Centre in Los Angeles with his infant son, Sire Jackson, on Sunday (03.08.14), when a member of his personal security team reportedly at...

Kim Kardashian is reportedly "actively trying to get pregnant" again.
The 33-year-old reality TV star, who recently claimed she is desperate to lose 20 pounds and get back to her pre-baby weight after welcoming her first child, North, into the world in June 2013, hopes to conceive a sibling for her 13-month-old daughter this year.
A source also told Us Weekly magazine: "Kim wants North to have a sibling who isn't too far apart in age."
News that Kim, who previously admitted she wants three children, is eager to expand her family with husband Kanye West comes less than one day after she vented her frustration about her current weight on Twitter.
She tweeted on Tuesday (05.08.14): "off to an intense workout. Can't seem to shake this last 15-20 lbs of baby weight. no more excuses. my baby is 1 years old! UGH (sic)."
She added: "I'm not gonna call it baby weight bc thats an excuse. i just gained weight & that's it. why is it so much harder to lose after baby though!! do any of u moms see their bodies just not the same? a different shape? ughhhh my hips & butt are huge now! they were big to begin with (sic)!"
Meanwhile, the 'Keeping Up with the Kardashians' star, who tied the knot in May, has reportedly purchased a new $20 million home with Kanye near her mother Kris Jenner's mansion in the Hidden Hills area of Los Angeles.
A source told gossip website TMZ.com that the couple, who are planning to sell their $11 million Beverly Hills house, as they are fed up of waiting for their extensive renovations to be completed, are now in escrow for the 3.5 acre estate, which was originally listed for $21 million and boasts two swimming pools, two vineyards and a 1,050 square foot entertainment pavilion.
The lavish house was previously owned by Lisa Marie Presley and the couple first fell in love with it a few months ago.

Kendra Wilkinson has allegedly consulted a divorce lawyer.
The 'Kendra On Top' star, who five year marriage to Hank Baskett was rocked by claims he had an affair with a transexual model while the blonde beauty was eight months pregnant with their second child earlier this year, is reportedly still trying to decide whether she and the 31-year-old former NFL star have a future together.
A source close to the 29-year-old Playboy model told Life & Style magazine: "Kendra's definitely looking into divorce. She's met with lawyers and is weighing her options."
The couple have yet to publicly acknowledge they are having issues, but Kendra has regularly been spotted out without her wedding ring since she kicked the gym owner out of their home in Calabasas, California in June.
But the duo, who have son, Hank IV, four, and daughter Alijah, two months, are still spending time together for the sake of their children.
The source said: "They're sort of stuck together now."
An insider previously claimed Kendra wanted to try to rebuild her relationship with Hank because she hated growing up in "a broken home."
The source said: "Kendra grew up in a broken home, so she always swore she'd never divorce.
"She is emotionally and financially invested in the relationship. She can't just walk away."

Alexis Bledel and Vincent Kartheiser have got married.
The 'Mad Men' co-stars, who got engaged in March 2013, secretly exchanged vows in a private ceremony in June.
A spokesperson for the former 'Gilmore Girls' actress, 32, told PEOPLE.com that they tied the knot in California.
The couple started dating after falling for each other on the set of the advertising drama in 2012 when Alexis joined the cast as Beth Dawes for a short stint.
A source previously said: "Vinnie basically fell in love with Alexis while she filmed a three-episode cameo. He was definitely smitten with her from the beginning."
While she was working on the series Alexis had nothing but praise for Vincent, 35.
She said at the time: "He's light and funny and has lots of energy on set. He keeps everybody energised as well."
Vincent also got advice from his co-stars Elisabeth Moss and Jessica Pare before he decided to propose to Alexis last year, and Elisabeth previously gushed: "They are such a yin and yang. I've known Vinny for 12 years and Alexis is just the sweetest. I've never seen Vincent like this. It is really cool."
Alexis was in a long-term relationship with former 'Heroes' star Milo Ventimiglia from December 2002 to July 2006.

Katie Holmes has no regrets about her time with ex-husband Tom Cruise.
The 35-year-old actress, who split from the 52-year-old actor in June 2012 after six years of marriage, insists she is "really grateful" for all of her experiences but prefers to focus on the future and caring for their daughter, Suri, eight.
Asked if she ever felt like making a deal to go back to the low-key life she had before she started dating the A-list actor in 2005, the 'Giver' star told Matt Lauer on the Today Show: "You know what? I never really look back. I just approach life [taking] it one day at a time. I'm really excited about where I am right now. I've had some really wonderful creative experiences. I'm just really grateful."
The brunette beauty blindsided the Scientologist when she divorced him amid reports she was concerned about how the sect would impact their daughter's life, and she admits trying to give Suri a normal childhood is still one of her top priorities.
She said: "Of course you try your best. I try very hard because I'm very grateful for my upbringing, my parents, my siblings. I try to do what they did for me for my little one."
She added: "The most important thing for me is letting her know how proud I am and her accomplishments mean everything. Whatever I do is whatever. It's really just about her. That's what I think is most important."

Mischa Barton admits her life and career aren't what she expected.
The 28-year-old actress regrets appearing on the TV series, 'The O.C.,' that propelled her to stardom in 2003 and wishes she had continued to focus on film projects.
Asked if she would do the show again, Mischa, who famously played Marissa Cooper on the hit FOX series, said: "Probably not."
She also told the UK's Metro newspaper: "It's something I came so close to not doing. I had a really great thing with film. People say be grateful for what you have but it [is] certainly not the kind of thing I was expecting it to be... I've kind of seen it all."
It was recently revealed that Mischa is on the verge of losing her eight-bedroom Beverly Hills mansion after missing five of her mortgage repayments, leaving her $100,000 in arrears.
The actress bought the property for $6.4 million, taking out a loan of $4.2 million, in 2005 and has been trying to sell up since 2010.
The Spanish-style property was first put on the market for $8.695 million and then listed it again after a brief break but failed to attract a buyer.
Mischa made it available for rent for $35,000 per month last year before putting it back on the market with the original price tag.

Naomi Watts feels more self-conscious about her looks as she gets older.
The 45-year-old actress, who has two sons, Kai, five, and Sasha, seven, with long-time partner Liev Schreiber, admits she is an "anxious person" and regularly thinks about going under the knife since moving to Los Angeles from New York City last year.
The 'Diana' star told the September issue of Town and Country magazine: "I'm really just feeling my way. This being an industry town, that self-consciousness just pervades."
She added: "There are days when I feel victorious that I have, you know, gotten this far [without plastic surgery]. But there are a million days when I look in the mirror and think, 'I'm going to do it.' "
Despite starring in dozens of films and TV shows, the Australian beauty only found fame when she was 33 and now wishes she had been more relaxed about being successful.
She said: "If only I'd known back then, over those ten years of trying to prove myself, what I know now - which is just be you. I didn't trust that me was what people wanted."
But the Oscar-nominated star still hates auditioning for roles.
The 'Impossible' star explained: "I hate being put in a position where I'm being tested. If I feel safe, I can be me, but if I don't feel safe, I try to please."